The present invention relates to a method of converting liquid microbiological substrate and apparatus for carrying out the method.
In the bio-chemical process technology, micro-organisms are frequently bred in a liquid nutrient substrate which is thereby converted. These conversions take place for example in a closed fermenter or in a bubble column, whilst in the case of aerobic processes a gas such as air or oxygen is introduced.
The apparatus employed for the conversion process should be such that optimal growth conditions result for the bacteria or fungii. It is known to generate a closed substrate circuit for the conversion process, in which the substrate continuously flows through a duct system. Employed as duct systems are vertically arranged fermenter devices, which are provided with a cylindrical outer shell in which a cylindrical inner shell is arranged. The substrate is then set in motion by a pump so that it rises between the outer and the inner shell and, at the top of the latter, overflows into the cavity bounded by the inner shell and flows back through this. In these circumstances, the fermenter device receives only such a quantity of substrate that a free space -- which can serve as degasification zone -- results in the upper part of the cavity bounded by the inner shell.
Some such known fermenter devices have the disadvantage that the breeding of cultures and the bio-chemical conversions often take an unduly long period.
It has now been found that the conversions can be accelerated in the case of anaerobic as well as aerobic processes, when the pressure of the substrate in the reaction zone alternationgly decreases and again increases along the flow path. In the case of anaerobic processes, the increase in the conversion speed is probably to be traced back to the fact that the cell walls of the micro-organisms are subjected by the pressure changes to a deformation movement, which promotes the exchange of material.
In the case of aerobic processes, the growth and reaction speed depends to a large extent upon the gas exchange of the micro-organisms, which is again dependent upon the quantity of gas liberated in the substrate and upon the size and the distribution of the gas bubbles. It has now been ascertained that aerobic processes, particularly, can be favourably influenced by pressure changes of the substrate. This might originate from the fact that gas bubbles change their diameter and their surface with changing substrate pressure, whilst turbulent gas flows can take place in the interior of the bubbles. This has the consequence, that the bubbles can more easily be opened on contact with the live cells.